1. Field of the Invention
The present invention relates generally to methods and systems for non-destructive testing and inspection of pipes, tubes, and other longitudinal cylindrical structures. The present invention relates more specifically to methods and systems for accurately positioning long-range torsional guided-wave inspection sensors on pipes, tubes, and other cylindrical structures to create partial excitation and detection around the pipe circumference.
2. Description of the Related Art
Long-range, guided-wave inspection technology is an emerging technology that has the capability of quickly surveying a large volume of a structure for defects and providing comprehensive condition information on the integrity of the structure. Using relatively low-frequency (typically under 100 kHz) guided-waves in the pulse-echo testing mode, this technology performs a 100% volumetric examination of a large area of a structure and detects and locates internal and external defects in the area around a given test position. In above-ground pipelines, for example, a test range of more than 500 feet can be achieved in one direction for detecting 2% to 3% defects from a given test position. In this case, percent refers to the circumferential cross-sectional area of the defect relative to the total pipewall cross section. This guided-wave inspection technology, including the magnetostrictive sensor (MsS) technology developed at Southwest Research Institute in San Antonio, Tex., is now widely used for testing piping networks in processing plants such as refineries and chemical plants. The preferred guided-wave mode for piping inspection is the torsional (T) wave.
For piping inspections, guided-wave probes that encircle the entire pipe circumference are presently in use. To install a guided-wave probe for piping inspection, the basic systems and methodologies require full access around the pipe circumference with about 3 to 5 inches of spacing. When access is limited to only a portion of the piping circumference, the long-range guided-wave inspection method is difficult to apply. Examples of limited access include pipelines placed very close to a wall and pipes or tubes placed closely together (such as with superheater and reheater tubes in boilers).
Examples of efforts that have been made in the past to provide systems and methods for positioning sensors in connection with the inspection of longitudinal cylindrical structures such as pipes and tubes include those disclosed in the following U.S. patents:
U.S. Pat. No. 4,916,394 issued to Thompson on Apr. 10, 1990 entitled Device for Adjustable Mounting of Magnetic Sensing Coils Used in Pipe Inspection describes a mounting shoe and a pair of adjustable contact wedges that may be moved in and out to accommodate the curvature of a pipe under inspection. The magnetic sensing coils in this case are protected by a shim that positions the coils in an optimum sensing range from the surface of the pipe.
U.S. Pat. No. 4,543,528 issued to Baraona on Sep. 24, 1985 entitled Flexible Probe Assembly for Use in Non-Destructive Testing of a Convex Workpiece Surface describes a complicated frame structure that includes a flexible array of sensor heads that are arranged in tension to conform to the pipe when directed against its convex surface. Multiple sensor heads are required in order to provide compliance with the curved surface of the pipe.
U.S. Pat. No. 6,373,252 issued to Eslambolchi et al. on Apr. 16, 2002 entitled Method and Apparatus Locating a Cable in a Pipe describes a system and method for locating a cable within the confines of a cylindrical pipe. In this case, the sensor placed in contact with the pipe is configured with an arcuate bottom surface that matches the curvature of the exterior circumference of the pipe. No specific mechanism is described for urging the curved surface of the detector head against the convex pipe surface.
U.S. Pat. No. 4,784,762 issued to Taliaferro entitled Magnetic Trap describes a method for positioning a Hall effect sensor on the external surface of a cylindrical pipe. The structure includes a magnetic trap positioned in conjunction with a magnetically transparent sheet on one side of which a magnet is mounted to produce a magnetic field. The Hall effect sensor is positioned adjacent the magnet to sense the magnetic field.
U.S. Pat. No. 3,568,049 issued to Barton on Mar. 2, 1971 entitled Adjustable Search Shoe for Use in Non-Destructing Testing of Tubular Members describes a sensor structure that includes an object engaging surface that may be mechanically adjusted to change its curvature so as to conform to the wall of the pipe or tubular object under inspection.
U.S. Pat. No. 5,841,277 issued to Hedengren et al. on Nov. 24, 1998 entitled Hand-Holdable Probe Having a Flexible Eddy Current Sensor describes a hand-held probe incorporating an eddy current sensor that can be moved across the surface being tested. The device is not specifically directed towards curved structures such as pipes or tubes, but instead describes a sensor with a generally planar bottom surface that has flexible or resilient characteristics. A primary objective of this device is to maintain an optimal standoff distance through the use of a flexible sensor/surface interface.
U.S. Pat. No. 4,510,447 issued to Moyer on Apr. 9, 1985 entitled Inspection Apparatus for Electro Magnetically Detecting Flaws in the Wall of the Pipe describes a large, complex structure that incorporates a moveable frame having a sensor urged against the surface of a pipe with a spring. The overall structure is a sensor assembly that establishes a closed magnetic circuit to generate a fluctuating magnetic field axially through the wall of the pipe between the poles of the electromagnet.
U.S. Pat. No. 6,812,707 issued to Yonezawa et al. on Nov. 2, 2004 entitled Detection Element for Objects and Detection Device Using the Same describes a sensor structure that includes a V-shaped engagement channel on a sensor head that incorporates an antenna coil wound around a magnetic member. The V-shaped channel facilitates positioning and placement of the sensor against the curved outer circumference of a pipe or tube.
U.S. Pat. No. 5,479,099 issued to Jiles et al. on Dec. 26, 1995 entitled Magnetic Inspection Heads Suited for Contoured or Irregular Surfaces describes an arrangement of coils associated with an array of moveable pins within an assembly that is positioned against the curved surface of a pipe or tube. The pins adjust their position according to contact with the external circumference of the pipe and thereby establish a conformed contact surface for the sensor on the magnetic inspection head.
In general, the prior efforts in the field have been directed to partial circumference sensor structures only where the type of interrogating signal is easily suited to such configurations. That is, none of the previous efforts at partial circumferential orientation have provided suitable sensor adherence structures for use in conjunction with long-rang torsional guided-waves. These interrogating waves have heretofore been limited to propagation from sensor structures that circumferentially surround the pipe or tube. No sensor structures have been designed that can take advantage of the volumetric inspection capabilities of long-range guided-waves where access to the entire circumference of the pipe or tube is restricted. It would be desirable, therefore to have a sensor structure, and a method for its implementation, that overcomes many of the problems of existing sensor structures and the requirement that they fully encircle the pipe or tube under inspection.
In the present invention, systems and methods for inspecting piping with limited access using partial excitation/detection around the pipe circumference are described. The systems and methods are built upon existing magnetostrictive sensor (MsS) methods and devices, particularly the thin magnetostrictive strip approach (described in U.S. Pat. No. 6,396,262, entitled Method and Apparatus for Short Term Inspection or Long Term Structural Health Monitoring; U.S. Pat. No. 6,429,650, entitled Method and Apparatus Generating and Detecting Torsional Wave Inspection of Pipes and Tubes; and U.S. Pat. No. 6,917,196, also entitled Method and Apparatus Generating and Detecting Torsional Wave Inspection of Pipes and Tubes, the disclosures of which are each incorporated herein in their entirety by reference) and the plate MsS probe (described in U.S. Pat. No. 6,294,912, entitled Method and Apparatus for Nondestructive Inspection of Plate Type Ferromagnetic Structures using Magnetostrictive Techniques, the disclosure of which is incorporated herein in its entirety by reference), but modified to fit the purposes of the present invention.